Gecl4 and/or sicl4 recovery process from optical fibers or glassy residues and process for producing sicl4 from sio2 rich materials

ABSTRACT

A method is provided for producing GeCl 4  with or without SiCl 4  from optical fibers, the method comprises the steps of: reacting comminuted optical fibers including germanium and optionally silicon oxides with a reagent including a solid carbonaceous reducing agent, chlorine and a boron compound to obtain a gaseous product including gaseous GeCl 4 , gaseous SiCl 4 , and gaseous BCl 3  in accordance with the reactions: 2BCl 3 (g)+1.5GeO 2 =1.5GeCl 4 (g)+B 2 O 3 ; 2BCl 3 (g)+1.5 SiO 2 =1.5 SiCl 4 (g)+B 2 O; B 2 O 3 +1.5C+3Cl 2 =2BCl 3 (g)+1.5CO 2 ; and then condensing the gaseous GeCl 4 , BCl 3  and optionally SiCl 4  into liquid GeCl 4 , BCl 3  and optionally SiCl 4 . The invention further provides a method for producing SiCl 4  (and optionally GeCl 4 ) from glass residues obtained from optical fiber manufacturing and wasted optical cables. The method includes the steps of: reacting comminuted glassy residues with a reagent including a solid carbonaceous reducing agent, a salt, a boron compound to obtain a gaseous product including SiCl 4 , BCl 3 , and optionally GeCl 4 ; and then condensing the gaseous SiCl4, BCl 3  (with or without GeCl 4 ) into liquid SiCl 4 , BCl 3  and GeCl 4 . There is also provided a method for producing SiCl 4  from a SiO 2  containing material.

FIELD OF THE INVENTION

The invention relates to a process for recovering germanium and siliciumfrom optical fibers and, more particularly, it relates to a process forrecovering germanium and silicium chlorides from optical fiberscontaining germanium and silicium oxides. The invention relates to aprocess for producing SiCl₄ from silicon oxides such as SiO₂ and to aprocess for concurrently producing SiCl₄ and GeCl₄ from glassy residuessuch as optical fibers.

DESCRIPTION OF THE PRIOR ART

Processes for manufacturing optical cables including optical fibers, asactive components for light signal transmission, are typically separatedin three major steps: a) preform manufacturing, b) optical fiberdrawing, and c) optical fiber cabling (Williams, 2000, The case of highpurity silicon and its application in IT and renewable energy,UNU/IAS,145 p.). Optical fibers have a core presenting a high refractiveindex surrounded by a cladding showing a lower refractive index (Alwayn,2004, Optical network design and implementation, Cisco Press, 840 p.).Often, the core is made of fused silica containing germanium oxide, usedas a doping agent, to increase the refractive index of silica. Thecladding is habitually made of pure silica.

The manufacturing of optical fibers is based on dechlorination reactionswere chlorides are transformed into oxides in a chemical reactor heatedat around 1000° C. The oxides are deposited on a solid support made ofsilica. Three main deposition systems exist (Williams, 2000). First, ina modified chemical vapor deposition (MCVD) process, the oxides aredeposited inside a high purity silica tube, the dechlorination reactionsare conducted until the tube is filled. The resulting glass rod issintered into a preform and the obtained preform is ready for thedrawing step. Second, an outside deposition system (ODS) uses a glassrod as a support where the oxide particles built up, the dechlorinationreactions are conducted until the desired rod diameter is reached. Therod is then sintered into a preform. Finally, the axial vapor deposition(AVD) process is somewhat similar to the ODS system, except that thebuilding up of the oxide material is conducted from a point as opposedto the entire rod length. The resulting soot is sintered into a preform.

The dechlorination reactions which occur in the MCVD process formanufacturing optical fibers made of SiO₂ and GeO₂ are (Tandon, 2005,Int. J. Appl. Ceram. Technol., 2, 6, 504-513):

SiCl₄(g)+2O₂(g)=SiO₂(s)+2Cl₂(g)   (1)

GeCl₄(g)+2O₂(g)=GeO₂(s)+2Cl₂(g)   (2)

For the ODS and AVD processes, the dechlorination reactions are(Williams, 2000):

SiCl₄(g)+O₂(g)+2H₂═SiO₂(s)+4HCl(g)   (3)

GeCl₄(g)+O₂(g)+2H₂═GeO₂+4HCl(g)   (4)

SiCl₄ and GeCl₄ are the starting chemical components for these threeprocesses.

By carefully choosing the adequate reagent mixture, preforms consistingof a core enriched in a given high refractive index oxide, surrounded bya cladding of pure silica are obtained from these processes. Thepreforms are placed on a vertical shaft. A small furnace melts the basaltip of the blank preform. The melted material is pulled as an opticalfiber which is coated and rolled up onto a spool (Yin and Jaluria, 1998,Trans. ASME, 120, 916-930).

The industry of optical fibers used extremely pure starting chloridesquoted as optical grade specification (99.999999 wt %, 6 decimal nines)in order to produce optical fibers made of pure oxides. Such purity isnecessary to assure no distortion of the optical signals transmitted(Alwayn, 2004). Because of the purity required, the chlorides used inthe dechlorination reactions are very expensive. This is specificallytrue for germanium tetrachloride, germanium being a scarce element inthe earth crust (Höll, R, Kling, M, Schroll, E: Metallogenesis ofgermanium—a review. Ore Geology Reviews 30 (2007), 145-180).

Manufacturing optical fibers produce important losses. An amount of highpurity glasses substantially equal to the amount of optical fiberproduced is defective or lost during the fabrication (Ma, Ogura,Kobayashi and Takahashi, Solar Energy Materials and Solar Cells, 2004,81, 477-483).

The optical fibers, often called the glassy components, contained inend-of-life cables are presently considered as a zero value component.When optical cable recycling is performed, the glassy components aredisposed in cement production furnaces or as raw material for civilengineering work (NTT Group, Environmental protection activity annualreport, 2004).

An efficient process is thus needed in order to recycle defectiveoptical fibers, losses of high purity glasses occurring duringmanufacturing of optical fibers, and optical fibers presents inend-of-life optical cables.

Japanese publication No. 2003-37904 by Takahashi reports the use of anovel thermal plasma system by which high purity SiO₂ from optical fiberresidues are converted to solar grade silicon (SOG-Si) used for theproduction of solar panels.

South Korean publication No. 2004-5357 by Jin, Kang and Lee instructs onthe recovery of non deposited SiO₂ during the preform filling. The nondeposited glassy particles are recovered on a glass particles collector.These particles are manufactured into a new preform using a specialinjection equipment.

Other patents listed below concern methods for dismantling opticalcables into their basic components and therefore they are not related tothe recovery of high-purity components from optical fibers.

Japanese publication No. 2004-38788 by Nakane teaches on the recyclingof plastics and rubbers from wasted optical cables for the recovery ofhigh-purity polyethylene and aluminum.

Japanese publication No. 2004-376291 by Ito, Usami and Masura, relatesto the separation of organic clad from optical fiber residues obtainedby segregation of optical cables. The process involves solventextraction and screening to obtain a clean quartz-glass materialrecycled as cement component and coated resins recycled as a solid fuel.

Japanese publication No. 2005-339701 by Ito, Usami and Masura, reportson the recycling of optical cables by crushing and sieving into usablematerials.

These three previous documents demonstrate that technologies areavailable to isolate the glassy components from optical cables. All ofthose approaches are based on low cost technologies such as crushing,sieving, and solvent extraction in order to isolate the glassycomponents from the other optical cable components.

Two publications, concerning the recycling of glassy residues,originating from the production of optical fibers or from end-of-lifeoptical cables, as high-purity products, have been located. These twopublications are derived from the Japanese Publication No. 2003-37904 byTakahashi on the recycling of high-purity glassy materials by a thermalplasma system. The first one by Ma, et al., (2004) presents thepreviously described technology. The second one by Ogura, Astuti,Yoshikawa, Morita and Takahashi (2004, Ind. Eng. Chem. Res., 43,1890-1893) describes a process using an arc-plasma furnace by which amixture of silicon carbide and silicon is obtained from a feed of wastedoptical fibers. When the silicon carbide product is recycled in theprocess furnace, the yield of high-purity silicon production increased.This process is run at very high temperature and produce silicon as afeedstock for the fabrication of solar panels.

In addition, Bohrer, Amelse, Narasimham, Tariyal, Turnipseed, Gill,Moebuis and Bodeker (1985, Journal of Light Wave Technology, LT-3, 3,699-705) have developed a process for the recovery of the unused GeCl₄in reactions (2) and (4) exiting the deposition system and present inthe process effluents. GeCl₄ is trapped into the gas scrubber as solublegermanate ions. After, a certain recirculation time to build up theconcentration, the germanate ions react with magnesium sulfate toprecipitate magnesium germanate which is filtered, dried, bagged andsold to a manufacturer.

U.S. Pat. No. 4,490,344 discloses BCl₃ as a chlorination agent for theformation of SiCl₄ from SiO₂.

BRIEF SUMMARY OF THE INVENTION

It is therefore an aim of the present invention to address the abovementioned issues.

According to a general aspect, there is provided a method for producingGeCl₄ from optical fibers; the method comprising the steps of: reactingcomminuted optical fibers including germanium oxides with a reagentincluding a solid carbonaceous reducing agent, chlorine and a boroncompound to obtain a gaseous product including gaseous GeCl₄, andgaseous BCl₃ in accordance with the reactions:

2BCl₃(g)+1.5GeO₂=1.5GeCl₄(g)+B₂O₃   (5)

B₂O₃+1.5C+3Cl₂=2BCl₃(g)+1.5CO₂; and   (7)

condensing the gaseous GeCl₄ and BCl₃ into liquid GeCl₄ and BCl₃.

According to another general aspect, there is provided a method forproducing GeCl₄ as starting components for optical fiber manufacturing.The method comprises the steps of: reacting comminuted optical fiberglassy residues including germanium and silicon oxides with a reagentincluding a solid carbonaceous reducing agent, chlorine and a boroncompound to obtain a gaseous product including gaseous GeCl₄, andgaseous BCl₃; condensing the gaseous GeCl₄ and BCl₃ into liquid GeCl₄and BCl₃.

According to a further general aspect, there is provided a method forchlorinating GeO₂ encapsulated into glasses. The method comprises thesteps of: reacting comminuted glasses with a reagent including a solidcarbonaceous reducing agent, chlorine and a boron compound to obtain agaseous product including gaseous GeCl₄, and gaseous BCl₃; andcondensing the gaseous GeCl₄ and BCl₃ into liquid GeCl₄ and BCl₃.

According to still another general aspect, there is provided a methodfor producing GeCl₄ from optical fibers. The method comprising the stepsof: reacting optical fibers including germanium oxides with a reagentincluding a reducing agent and BCl₃ to obtain a gaseous productincluding gaseous GeCl₄, and gaseous BCl₃; and condensing the gaseousGeCl₄ and BCl₃ into liquid GeCl₄ and BCl₃.

According to another aspect, there is provided the methods for producingGeCl₄ from optical fibers, optical fibers glassy residues or any otherGeO₂ containing residues as defined above, wherein the residues alsocontain SiO₂, the method comprising the steps of: reacting residuesincluding germanium and silicon oxides with a reagent including a solidcarbonaceous reducing agent, chlorine and a boron compound to obtain agaseous product including gaseous GeCl₄, gaseous SiCl₄, and gaseous BCl₃in accordance with the reactions:

2BCl₃(g)+1.5GeO₂=1.5GeCl₄(g)+B₂O₃   (5)

2BCl₃(g)+1.5SiO₂=1.5SiCl₄(g)+B₂O₃   (6)

B₂O₃+1.5C+3Cl₂=2BCl₃(g)+1.5CO₂;   (7)

condensing the gaseous GeCl₄, SiCl₄ and BCl₃ into liquid GeCl₄, SiCl₄and BCl₃.

According to a further aspect of the invention, the is provided themethods as defined above wherein the liquid GeCl₄ and/or liquid SiCl₄and/or liquid BCl₃ are separated by fractional distillation.

According to a general aspect, there is provided a method for producingGeCl₄ and SiCl₄ from optical fibers, the method comprising the steps of:reacting comminuted optical fibers including germanium and siliconoxides with a reagent including a solid carbonaceous reducing agent,chlorine and a boron compound to obtain a gaseous product includinggaseous GeCl₄, gaseous SiCl₄, and gaseous BCl₃ in accordance with thereactions:

2BCl₃(g)+1.5GeO₂=1.5GeCl₄(g)+B₂O₃   (5)

2BCl₃(g)+1.5SiO₂=1.5SiCl₄(g)+B₂O₃   (6)

B₂O₃+1.5C+3Cl₂=2BCl₃(g)+1.5CO₂;   (7)

firstly condensing the gaseous GeCl₄ into liquid GeCl₄ by loweringgaseous product temperature below GeCl₄ condensing temperature and aboveSiCl₄ condensing temperature; and secondly condensing the gaseous SiCl₄into liquid SiCl₄ by lowering gaseous product temperature below SiCl₄condensing temperature and above BCl₃ condensing temperature.

According to another general aspect, there is provided a method forproducing GeCl₄ and SiCl₄ as starting components for optical fibermanufacturing. The method comprises the steps of: reacting comminutedoptical fiber glassy residues including germanium and silicon oxideswith a reagent including a solid carbonaceous reducing agent, chlorineand a boron compound to obtain a gaseous product including gaseousGeCl₄, gaseous SiCl₄, and gaseous BCl₃; firstly condensing the gaseousGeCl₄ into liquid GeCl₄ by lowering gaseous product temperature belowGeCl₄ condensing temperature and above SiCl₄ condensing temperature; andsecondly condensing the gaseous SiCl₄ into liquid SiCl₄ by loweringgaseous product temperature below SiCl₄ condensing temperature and aboveBCl₃ condensing temperature.

According to a further general aspect, there is provided a method forchlorinating GeO₂ encapsulated into SiO₂ glasses. The method comprisesthe steps of: reacting comminuted SiO₂ glasses with a reagent includinga solid carbonaceous reducing agent, chlorine and a boron compound toobtain a gaseous product including gaseous GeCl₄, gaseous SiCl₄, andgaseous BCl₃; and condensing the gaseous GeCl₄ into liquid GeCl₄ bylowering gaseous product temperature below GeCl₄ condensing temperatureand above SiCl₄ condensing temperature.

According to still another general aspect, there is provided a methodfor producing GeCl₄ and SiCl₄ from optical fibers. The method comprisingthe steps of: reacting optical fibers including germanium and siliconoxides with a reagent including a reducing agent and BCl₃ to obtain agaseous product including gaseous GeCl₄, gaseous SiCl₄, and gaseousBCl₃; and condensing the gaseous GeCl₄ into liquid GeCl₄ by lowering thegaseous product temperature below GeCl₄ condensing temperature and aboveSiCl₄ condensing temperature.

According to a further general aspect, there is provided a method forproducing SiCl₄ from optical fiber glassy residues, the methodcomprising the steps of: reacting comminuted optical fiber glassyresidues with a reagent including a solid carbonaceous reducing agent, asalt selected from the group consisting of KCl, CsCl, and RbCl, and aboron compound to obtain a gaseous product including gaseous SiCl₄ inaccordance with the reactions:

4BCl₄ ⁻(I)+SiO₂+C═SiCl₄(g)+4BCl₃(g)+CO₂   (9)

and condensing the gaseous SiCl₄ and BCl₃ into liquid SiCl₄ and BCl₃.Optionally, chlorine gas can be added as reagent.

Still, according to a further general aspect, there is provided a methodfor producing SiCl₄, and optionally GeCl₄ from optical fiber glassyresidues, the method comprising the steps of: reacting comminutedoptical fiber glassy residues with a reagent including a solidcarbonaceous reducing agent, a salt selected from the group consistingof: KCl, CsCl and RbCl, a boron compound and, optionally chlorine toobtain a gaseous product including gaseous SiCl₄ and optionally GeCl₄ inaccordance with the reactions:

4BCl₄ ⁻(I)+GeO₂+C═GeCl₄(g)+4BCl₃(g)+CO₂   (8)

4BCl₄ ⁻(I)+SiO₂+C═SiCl₄(g)+4BCl₃(g)+CO₂   (9)

and condensing the gaseous SiCl₄, GeCl₄ if present, and BCl₃ into liquidSiCl₄, GeCl₄ and BCl₃.

According to a further general aspect, there is provided a method forproducing SiCl₄ and GeCl₄ from optical fiber glassy residues, the methodcomprising the steps of: reacting comminuted optical fiber glassyresidues with a reagent including a solid carbonaceous reducing agent, asalt selected from the group consisting of KCl, CsCl, and RbCl, chlorineand a boron compound to obtain a gaseous product including gaseous GeCl₄and gaseous SiCl₄ in accordance with the reactions:

4BCl₄ ⁻(I)+GeO₂+C═GeCl₄(g)+4BCl₃(g)+CO₂   (8)

4BCl₄ ⁻(I)+SiO₂+C═SiCl₄(g)+4BCl₃(g)+CO₂   (9)

firstly condensing the gaseous GeCl₄ into liquid GeCl₄ by loweringgaseous product temperature below GeCl₄ condensing temperature and aboveSiCl₄ condensing temperature; and secondly condensing the gaseous SiCl₄into liquid SiCl₄ by lowering gaseous product temperature below SiCl₄condensing temperature and above BCl₃ condensing temperature.

According to another general aspect, there is provided a method forproducing GeCl₄ and SiCl₄ as starting components for optical fibermanufacturing. The method comprises the steps of: reacting comminutedoptical fiber glassy residues with a reagent including a solidcarbonaceous reducing agent, a salt selected from the group consistingof KCl, CsCl, and RbCl, chlorine and a boron compound to obtain agaseous product including gaseous GeCl₄ and gaseous SiCl₄; firstlycondensing the gaseous GeCl₄ into liquid GeCl₄ by lowering gaseousproduct temperature below GeCl₄ condensing temperature and above SiCl₄condensing temperature; and secondly condensing the gaseous SiCl₄ intoliquid SiCl₄ by lowering gaseous product temperature below SiCl₄condensing temperature and above BCl₃ condensing temperature.

According to a further general aspect, there is provided a method forproducing SiCl₄ from a SiO₂ containing material. The method comprisesthe steps of: reacting a comminuted SiO₂ containing material with areagent including a solid carbonaceous reducing agent, a salt selectedfrom the group consisting of KCl, CsCl, and RbCl, chlorine and a boroncompound to obtain a gaseous product including gaseous SiCl₄; andcondensing the gaseous SiCl₄ into liquid SiCl₄ by lowering gaseousproduct temperature below SiCl₄ condensing temperature and above BCl₃condensing temperature.

According to still another general aspect, there is provided a methodfor producing SiCl₄ from glassy residues. The method comprising thesteps of: reacting glassy residues with a solid carbonaceous reducingagent, a salt selected from the group consisting of KCl, CsCl, and RbCl,chlorine and a boron compound to obtain a gaseous product includinggaseous SiCl₄; and condensing the gaseous SiCl₄ into liquid SiCl₄ bylowering the gaseous product temperature below SiCl₄ condensingtemperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram of the process in accordance with anembodiment, with a reagent including B₂O₃ doped activated charcoal;

FIG. 2 is a flow diagram of the process in accordance with anotherembodiment, with a reagent including gaseous BCl₃;

FIG. 3 is a flow diagram of a SiO₂ and GeO₂ chlorination process inaccordance with an embodiment, with a reagent including B₂O₃ dopedactivated charcoal;

FIG. 4 is a flow diagram of the SiO₂ and GeO₂ chlorination process inaccordance with another embodiment, with a reagent including activatedcharcoal;

FIG. 5 is a flow diagram of the SiO₂ chlorination process in accordancewith still another embodiment, with a SiO₂ rich feed material;

FIG. 6 is a flow diagram of the SiO₂ chlorination process in accordancewith still another embodiment, with a SiO₂ rich feed material;

FIG. 7 is a schematic perspective view of an experimental set up inaccordance with an embodiment; and

FIG. 8 is a schematic perspective view of the experimental set up shownin FIG. 7, showing the position of a sample beaker.

It will be noted that throughout the appended drawings, like featuresare identified by like reference numerals.

DETAILED DESCRIPTION

Referring to the drawings and, more particularly, referring to FIGS. 1and 2, processes for producing concurrently germanium tetrachloride andsilicon tetrachloride from optical fibers are described. In theprocesses, germanium and silicon oxides (GeO₂ and SiO₂) present inoptical fibers are converted into germanium and silicon chlorides (GeCl₄and SiCl₄). The produced chlorides are identical to those commonlyemployed in the manufacture of optical fibers.

For instance, the optical fibers, as feed material 10, can be glassyresidues originating from optical fiber production, i.e. glassy residuesoriginating from optical fiber production facilities or oxides particlescarry over in a scrubber unit of optic fiber production facilities, orglassy residues originating from end-of-life optical fibers, i.e.optical fibers originating from the dismantling of used optical cables.

The glassy residues, as feed material 10, are first dried and comminutedbefore being introduced in a chlorination reactor 14. The glassyresidues can be either crushed or shredded to particles having anaverage size ranging between micrometers to millimeters. For instance,the particle average size can range between 10 and 250 μm. In anembodiment, the particles have a substantially uniform size.

These glassy residues can have a resin coating. This resin coating doesnot negatively interfere in the GeCl₄ and SiCl₄ manufacturing process.On the opposite, the resin coating can have a positive effect on theprocess as the organic coating can be used as a reducer during thecarbochlorination process.

Chlorination and Prior Preparing Steps

As mentioned above, for manufacturing optical fibers, the dechlorinationreactions (1) to (4) are carried out. To recover silicon and germaniumcontained in the glassy residues as oxides, these reactions arereversed.

According to another aspect of the invention, boron trichloride is usedas the effective chlorination agent for GeO₂ and SiO₂. Moreparticularly, the following reactions take place:

2BCl₃(g)+1.5GeO₂=1.5GeCl₄(g)+B₂O₃   (5)

2BCl₃(g)+1.5 SiO₂=1.5 SiCl₄(g)+B₂O₃   (6)

B₂O₃+1.5C+3Cl₂=2BCl₃(g)+1.5CO₂   (7)

The action of BCl₃ on SiO₂ to produce SiCl₄ and B₂O₃ is recognized at atemperature around 350° C. (Kroll, Metal Industry, 1952, 81, (13),243-6; Savel'ev et al., Neorganicheskie Materialy, 1973, 9, (2), 325-6).Moreover, B₂O₃ can be chlorinated (or regenerated) as BCl₃ by the actionof Cl₂ and a reducing agent such as coke or activated charcoal (Alam etal., 2004, Kirk-Othmer Encyclopedia of chemical technology, 138-168).

To recover silicon and germanium contained in the glassy residues asoxides, BCl₃ is now used as effective chlorination agent in a relativelylow temperature process. More particularly, BCl₃ is a chlorinating agentfor GeO₂ encapsulated into SiO₂ glasses. Therefore, the above-mentionedreactions can be used to simultaneously produce GeCl₄ and SiCl₄ fromoptical fiber glassy residues containing silicium and germanium oxides.

As it will be described in more details below, BCl₃ can be added as agas or can be generated in situ through reaction (7).

For carrying out the chlorination reactions, a reagent mixture includinga reducing agent 22, 122, chlorine (Cl₂) 23, 123 and boron 16, 116 isprovided in addition to the glassy residue feed material 10 (FIGS. 1 &2).

The reducing agent can be a solid carbonaceous reducing agent such asmetallurgical coke or activated carbon, for instance.

Referring to FIG. 1, there is shown that, in an embodiment, the reducingagent and boron of the reagent mixture are provided as a reducing agentdoped with a boron compound 12. More particularly, a boron compound isadsorbed on a solid reducer prior to the chlorination step 14. In theembodiment shown, the solid reducer 22 is activated charcoal. As it willbe described in more details below, high conversion rates for GeO₂ andSiO₂ were obtained when the reagent mixture included the reducing agentwith the adsorbed boron compound.

The reducing agent with the adsorbed boron compound 12 is obtained froma solution saturated with a boron compound 16, such as H₃BO₃, forinstance. In an agitated tank 20, the saturated solution is mixed withthe solid reducing agent 22, such as activated charcoal, for instance.The solid carbonaceous reducer containing the adsorbed boron compound isseparated by filtration 24, for instance, from the solution 26 and canbe dried 28 at a temperature of 500° C. for three hours. In an alternateembodiment, the solid carbonaceous reducer containing the adsorbed boroncompound can be dried at a temperature ranging between 450 and 550° C.for 30 minutes to three hours.

The drying step 28 can be carried out in an inert atmosphere such aswith nitrogen, for instance. The drying step 28 removes any form ofwater which could be detrimental to the chlorination process.

The adsoption, filtration and drying steps 20, 24, 28 are usuallycarried outside the chlorination reactor.

Referring now to FIG. 2, there is shown that, in an alternateembodiment, the reducing agent 122, such as activated charcoal forinstance, and boron 116 are distinctly provided. Instead of beingadsorbed on the reducing agent 122, boron is provided separately asgaseous BCl₃ 116.

Now referring simultaneously to FIGS. 1 and 2, there is shown that thechlorination reaction is carried out in a chlorination reactor 14 at atemperature ranging between 450 and 1100° C. In an embodiment, thereactor 14 is made from a material resisting to the corrosive nature ofgases contained therein.

In the chlorination reactor 14, a gaseous product 30 is obtained. Thegaseous product 30 includes, amongst other, gaseous GeCl₄ and SiCl₄. Acontinuous chlorine flow (Cl₂) is maintained in the chlorination reactorand GeCl₄ and SiCl₄ leave the chlorination reactor 14 as vapor phasesand are carried out by the gaseous product flow toward the condensationsections 32, 34, 36. The gaseous product 30 leaving thecarbochlorination reactor 14 is essentially composed of GeCl₄, SiCl₄,Cl₂, BCl₃, and CO₂.

At the exit of the carbochlorination reactor 14, the gaseous product 30and the solid reducer 222 are separated via a filtration system (notshown). The solid reducer 222 is collected in a receiving bin and isreused in the chlorination process as reducing agent.

The gaseous product 30 is collected in a pipe system connecting thechlorination reactor 14 to a first condensing unit 32. The pipe systemis thermostated, i.e. the gas temperature inside the pipe system iscontrolled. Thus, the temperature can be maintained over the boilingtemperature of GeCl₄ (84° C.), one gaseous product component. Theboiling points of the other gaseous product components exiting thecarbochlorination reactor 14 are lower than GeCl₄ boiling point. Thus,all gaseous product components remain in gaseous phase in the pipesystem extending between the chlorination reactor 14 and the firstcondensing unit 32.

First Condensing Unit: GeCl4

The first condensing unit 32 condenses selectively GeCl₄(g) from theother gaseous product components and, more particularly, SiCl₄(g),BCl₃(g), Cl₂(g), CO₂(g).

To perform this selective condensation of GeCl₄, the temperature insidethe condenser 32 is set to a set-point slightly below GeCl₄ boilingpoint and slightly above SiCl₄ boiling point (57.6° C.). The gaseousproduct 30 is cooled and washed with liquid GeCl₄ 38.

The condenser 32 is filled with perforated spheres made of a resistantmaterial. A recycling loop of liquid GeCl₄ connected to a shower nozzle,placed at the top of the unit, assures adequate percolation and contactsbetween the liquid phase 38 and the gaseous product 30. The condensedliquid GeCl₄ 40 is collected in a reservoir placed at the base of thecondensing unit 32. The gaseous product 42 exiting the condenser 32 isessentially composed of SiCl₄(g), BCl₃(g), Cl₂(g), and CO₂(g). It isdirected via a second pipe system to a second condensing unit 34 wheregaseous SiCl₄ is condensed, as it will be described in more detailsbelow.

As for the first pipe system extending between the chlorination reactor14 to the first condensing unit 32, the second pipe system isthermostated. Thus, the temperature can be maintained over SiCl₄ boilingtemperature (57.6° C.) and below GeCl₄ boiling point (84° C.). Thus, allgaseous product components remain in gaseous phase in the second pipesystem extending between the first and the second condensing units 32,34.

Second Condensing Unit: SiCl₄

This second condensing unit 34 is similar to the first condensing unit32, except that the temperature inside the condenser 34 is set to apoint slightly below SiCl₄ condensation point and that the gaseousproduct 42 entering the condenser 34 is washed with SiCl₄ in liquidphase 44. These operating conditions allow the selective condensation ofSiCl₄ 46 which is collected in a reservoir located at the base of thecondensing equipment 34. Hence, the gaseous product 48 exiting thesecond condenser 34 essentially includes BCl₃(g), Cl₂(g), CO₂(g). It isdirected towards a third condensing unit 36 where the condensation ofBCl₃ is carried out through a third pipe system.

As for the previous pipe systems, the third pipe system is thermostatedand its temperature is maintained over BCl₃ boiling temperature (12.5°C.) and below SiCl₄ boiling point (57.6° C.). Thus, BCl₃(g), Cl₂(g),CO₂(g), the gaseous product components, remain in gaseous phase in thethird pipe system extending between the second and the third condensingunits 34, 36.

Third Condensing Unit: BCl₃

In the third condensing unit 36, gaseous BCl₃ is condensed. Thetemperature inside the condenser 36 is adjusted to a set-point slightlybelow the condensation point of BCl₃ and the gas entering the condenser36 is washed with liquid BCl₃ 50 allowing its selective condensation.The gaseous product 52 exiting the condenser 36 includes Cl₂(g) andCO₂(g) and it is directed towards a scrubbing and a neutralizationsystems 54.

Liquid BCl₃ 56 obtained at this condensation step can be recycled as areagent 223 to the chlorination reactor 14 after a gasification step 58.The quantity of recycled BCl₃ 223 used to chlorinate the optical fiberfeed 10 is balanced with additional input of BCl₃ 116 or solid boroncompound 16, if necessary.

Scrubbing and Neutralization

Chlorine (Cl₂) is removed from the gaseous product 52 in a scrubber 54.This scrubbing unit 54 includes a vertical cylinder containingperforated plastic spheres. The scrubber 54 is filled to a certainextend with a solution of NaOH 60. A system, including a pump linked toa recycling loop and a spray nozzle located at the top of the scrubber54, allows the gaseous product 52 to be washed and contacted with theNaOH solution 60. The following reaction occurs between chlorinecontained in the gaseous product 52 and the NaOH solution 60:

Cl₂(g)+2NaOH═NaOCl+NaCl+H₂O.   (8)

The pH of the solution is controlled by an exterior supply ofconcentrated NaOH. The NaOCl solution 62 resulting from the scrubbingprocedure is subsequently treated with H₂O₂ 64, in an agitated tank 66,in order to obtain a sodium chloride solution 68 by the reaction

NaOCl+H₂O₂═NaCl+H₂O+O₂.   (9)

The gas exiting at the top of the scrubber contains essentially CO₂ 70.If necessary, the CO₂ 70 exiting the process can be trapped orneutralized by an existing complementary technology aiming at CO₂emanation recovery.

Cl₂ Compressor

In an alternate embodiment, the chlorine scrubber unit 54 can bereplaced by a chlorine compressor which allows compression of gaseouschlorine into a liquid chlorine and therefore its separation fromgaseous CO₂. The compressed chlorine can be stored in gas cylinders forfuture uses such as one of the chlorination process reactant.

Liquid GeCl₄ and Liquid SiCl₄

The process described above transforms optical fibers glassy residues inchloride forms which can be directly used as feed material formanufacturing optical fibers. The liquid chlorides selectively separatedduring the process and collected at the base of the GeCl₄ condenser andthe SiCl₄ condenser are of relatively high purity.

If necessary, additional purification steps can be performed on theseparated chlorides obtained from the process. These additionalpurification steps can include one or several methods such asdistillation, fractional distillation, solvent extraction and resinpurification.

Alternative Embodiment

Referring to the drawings and, more particularly, referring to FIGS. 3to 5, processes for producing chlorides from oxide containing feedmaterials are described. More particularly, in FIGS. 3 and 4, processesfor producing concurrently germanium tetrachloride and silicontetrachloride from optical fiber glassy residues are described. In theprocesses, germanium and silicon oxides (GeO₂ and SiO₂) present inoptical fibers or other glassy residues are converted into germanium andsilicon tetrachlorides (GeCl₄ and SiCl₄). The produced tetrachloridesare identical to those commonly employed in the fabrication of opticalfibers. In FIG. 5, a process for producing silicon tetrachloride from aSiO₂-rich material is described. The silicon oxide (SiO₂) presents inthe SiO₂-rich material is converted into silicon tetrachloride (SiCl₄).

For instance, the optical fibers, as feed material 10, can be glassyresidues originating from optical fiber production, i.e. glassy residuesoriginating from optical fiber production facilities or oxide particlescarry over in a scrubber unit of optic fiber production facilities,glassy residues originating from end-of-life optical fibers, i.e.optical fibers originating from the dismantling of used optical cables,or glassy residues isolated from wasted optical cables.

These glassy residues, as feed material, can have a resin coating. Thisresin coating does not negatively interfere in the GeCl₄ and SiCl₄manufacturing process. On the opposite, the resin coating can have apositive effect on the process as the organic coating can be used as areducer during the carbochlorination process.

In an alternate embodiment, the feed material 110 (see FIG. 5) caninclude a SiO₂-rich material which is substantially free of GeO₂, suchas quartz, and which will be converted into SiCl₄ in a chlorinationreactor 14. In an embodiment, the SiO₂-rich material includes more than90 wt % of SiO₂. For SiO₂ rich feed substantially free of GeO₂, thefractional distillation step is simplified since no GeCl₄ is present inthe mixture. If necessary a primary condensing unit can be added at theexit of the reactor to remove unwanted high boiling points chlorideimpurities.

Prior Preparing Steps

The feed material 10, 110, either the glassy residues or the SiO₂-richmaterial, are first dried and comminuted before being introduced in achlorination reactor 14. The feed material 110 can be either crushed,grinded, or shredded to particles having an average size ranging betweenmicrometers to millimeters. For instance, the particle average size canrange between 10 and 250 μm. In an embodiment, the particles have asubstantially uniform size.

In an alternate embodiment, the grinded feed material 10, 110 isintroduced in the reactor 14 without being previously dried. The dryingstep can be carried out within the reactor 14 or the process can bedrying step free. The feed material 10, 110 can be dried at atemperature ranging between 400 and 600° C. for 0.5 hour to 3 hours, forinstance. Moreover, the reagent mixture or only a portion thereof can beintroduced in the reactor 14 while carrying the drying step, as it willbe described in more details below. The drying step can be carried outin an inert atmosphere such as under nitrogen, for instance. The dryingstep removes any form of water which could be detrimental to thechlorination process.

Chlorination

As mentioned above, for manufacturing optical fibers, the dechlorinationreactions (1) to (4) are carried out. To recover silicon and germaniumcontained in the glassy residues as oxides, these reactions are reversedin a chlorination procedure.

For carrying out the chlorination reactions, a reagent mixture includinga reducing agent 12, 22, a salt 27 such as KCl, RbCl, and CsCl, chlorine(Cl₂) 23 and a boron compound, either B₂O₃ (FIG. 3) or boron trichloride(BCl₃) 29 (FIGS. 4 and 5), is provided in addition to the feed material10, 110, either the glassy residues or the SiO₂-rich material. In FIGS.3 to 5, the salt of the reagent mixture is KCl. The salt mass represents3 to 15 wt % of the total solid feed mass, i.e. the feed material mass,the reducing agent mass, and the salt mass. Particularly, KCl is used.More particularly, when KCl is used, chlorine gas (Cl₂) may be omittedwith still excellent results.

The reducing agent 12, 22 can be a solid carbonaceous reducing agentsuch as metallurgical coke or activated carbon/charcoal, for instance.The ratio between the reducing agent mass and the feed material massvaries between 0.3 and 1.

In an embodiment, a portion of the reagent mixture is added to thecomminuted feed material 10, 110 before carrying out the drying step.For instance and without being limitative, the reducing agent 12, 22 andthe salt 27, i.e. the solid components of the reagent mixture, can beadded to the comminuted feed material 10, 110 before carrying out thedrying step. As mentioned above, the drying step can be carried out at atemperature ranging between 400 and 600° C. for 0.5 hour to 3 hours, forinstance. Once the drying step is terminated, the other components (Cl₂and BCl₃) of the reagent mixture are added to the dried solidcomponents.

Referring now to FIG. 3, there is shown that, in an embodiment, thereducing agent 12 is provided as a reducing agent doped with a boroncompound and the feed material 10 includes glassy residues. Moreparticularly, the boron compound is adsorbed on a solid reducer prior tothe chlorination step 14. In the embodiment shown, the solid reducer 22is activated charcoal.

The reducing agent with the adsorbed boron compound 12 is obtained froma solution saturated with a boron compound 16, such as H₃BO₃, forinstance. In an agitated tank 20, the saturated solution is mixed withthe solid reducing agent 22, such as activated charcoal, for instance.The solid carbonaceous reducer containing the adsorbed boron compound isseparated by filtration 24, for instance, from the solution 26 and canbe dried 28 at a temperature of 500° C. for three hours. In an alternateembodiment, the solid carbonaceous reducer containing the adsorbed boroncompound can be dried at a temperature ranging between 450 and 550° C.for 30 minutes to three hours. The drying step 28 can be carried out inan inert atmosphere such as with nitrogen, for instance. The drying step28 removes any form of water which could be detrimental to thechlorination process.

The adsorption, filtration and drying steps 20, 24, 28 are usuallycarried outside the chlorination reactor 14. In this embodiment, thereagent does not compulsorily include a fresh BCl₃ supply 29 (see FIGS.4 and 5). However, as it will be described in more details below,recycled BCl₃ can be added to the reagent.

Referring now to FIG. 4, there is shown that, in an alternateembodiment, the reducing agent 22, such as activated charcoal forinstance, is distinctly provided from boron. In this case, a fresh BCl₃supply 29 is added to the reagent. As for the embodiment described abovein reference to FIG. 3, the feed material includes glassy residues.

Referring now to FIG. 5, there is shown that, in an another alternateembodiment, the feed material 110 includes a SiO₂-rich material and thereducing agent 22, such as activated charcoal for instance, isdistinctly provided from boron. In the embodiment shown in FIG. 5 anddescribed below, the reagent includes a fresh BCl₃ supply 29. It isappreciated that, in an alternate embodiment, a reducing agent dopedwith a boron compound can also be used with a SiO₂-rich feed material.

Now referring simultaneously to FIGS. 3 to 5, there is shown that thechlorination reaction is carried out in a chlorination reactor 14 at atemperature ranging between 450 and 1100° C. and, in an alternateembodiment, the temperature is ranging between 750 and 950° C. In anembodiment, the reactor 14 is made from a material resisting to thecorrosive nature of gases contained therein.

In the chlorination reactor 14, a gaseous product 30 is obtained. Thegaseous product 30 includes, amongst other, gaseous GeCl₄ and SiCl₄ ifthe feed material 10 includes glassy residues (FIGS. 3 and 4) or gaseousSiCl₄ if the feed material 110 includes a SiO₂-rich material (FIG. 5). Acontinuous chlorine flow (Cl₂) 23 is maintained in the chlorinationreactor and the gaseous product 30, including gaseous SiCl₄ and GeCl₄,if any, leaves the chlorination reactor 14 as vapor phase and is carriedout toward the condensation sections 32, 34, 36, 132, as it will bedescribed in more details below. The gaseous product 30 leaving thecarbochiorination reactor 14 is essentially composed of GeCl₄, SiCl₄,Cl₂, BCl₃, and CO₂ if the feed material includes glassy residues (FIGS.3 and 4) and SiCl₄, Cl₂, BCl₃, CO₂, and possibly other chlorideimpurities, if the feed material includes a SiO₂-rich material (FIG. 5).

Muetterties (Journal of the American Chemical Society, 1957, vol., 79,6563-6564) have demonstrated that tetrachloroborate salts of the typeKBCl₄, RbBCl₄ and CsBCl₄ can be prepared by reacting at high temperaturean appropriate salt such as KCl with gaseous BCl₃.

In the chlorination reactions of the process, BCl₄ ⁻ is used as theeffective chlorinating agent for SiO₂ glasses and GeO₂ glasses containedin optical fibers and for SiO₂ contained in SiO₂-rich material. Moreparticularly, the following reactions take place to simultaneouslyproduce GeCl₄ and SiCl₄ from glassy residues:

KCl+BCl₃(g)=K⁺+BCl₄ ⁻(I)   (10)

4BCl₄ ⁻(I)+GeO₂+C═GeCl₄(g)+4BCl₃(g)+CO₂   (11)

4BCl₄ ⁻(I)+SiO₂+C═SiCl₄(g)+4BCl₃(g)+CO₂   (12)

If the feed material is substantially free of GeO₂, the same reactionstake place, except reaction (11).

The reactions are carried out at a temperature ranging between 450 and1100° C., in an alternate embodiment, at a temperature ranging between800 and 900° C., and, in still an alternate embodiment, at a temperatureranging between 825 and 875° C.

At a temperature proximate to 850° C., KBCl₄ is in liquid phase sincethis temperature is above the melting point of KCl (776° C.). The oxideand carbon particles are probably partially surrounded by a liquid bathcontaining K⁺ and BCl₄ ⁻ ions. The BCl₄ ⁻ ion being the chlorinatingagent, Cl⁻ is transferred to the oxide surface via the reactions (11)and (12) which lead to the production of a gaseous phase including BCl₃,SiCl₄, GeCl₄, if any, and CO₂, which escapes the KBCl₄ liquid bath.Then, gaseous BCl₃ enters the reactor gaseous atmosphere in which a flowof BCl₃ and Cl₂ is maintained. BCl₃ is a strong Lewis acid (Alam et al.,2004, Kirk-Othmer Encyclopedia of chemical technology, 138-168) andtherefore a portion of BCl₃ reacts with Cl₂ to give:

BCl₃(g)+Cl₂(g)=BCl₄ ⁻+Cl⁺  (13)

The ion BCl₄ ⁻ can then reenter the liquid bath by, using ion K⁺, fromreaction (10):

K⁺+BCl₄ ⁻═KBCl₄   (14)

The ion Cl⁺ produced at reaction (13) is probably reacting with theexposed surfaces of a carbonaceous reducing agent (metallurgical coke,graphite or activated charcoal) at active sites where a high density ofunpaired electrons are present (Bandosz and Ania, in: Activated carbonsurfaces in environmental remediation, Elsevier 2006, p. 159-229), asillustrated by:

Cl⁺+C(negatively charged active sites)=C—Cl   (15)

In the reactor 14 where reactions are conducted, GeCl₄, if any, andSiCl₄ are present as gases. Since a continuous flow of Cl₂ 23 ismaintained in the system, GeCl₄, if any, and SiCl₄ leave the reactor asvapor phases and are carried out by the gas flow toward the condensationsections of the process, which will be described in more details below.The gases leaving the carbochiorination reactor 14 include GeCl₄, ifany, SiCl₄, Cl₂, BCl₃, and CO₂.

The gaseous product 30 and the solid reducer 22 are separated via agas/solid separator (not shown). The solid reducer 22 is collected in areceiving bin and is reused in the chlorination process as reducingagent.

To recover silicon and germanium contained in the glassy residues asoxides, BCl₄ ⁻ is used as effective chlorination agent in a relativelylow temperature process. More particularly, BCl₄ ⁻ is a chlorinatingagent for GeO₂ encapsulated into SiO₂ glasses. Therefore, theabove-mentioned reactions can be used to simultaneously produce GeCl₄and SiCl₄ from optical fiber glassy residues containing silicium andgermanium oxides. BCl₄ ⁻ is also a chlorination agent for SiO₂ inSiO₂-rich feed material to produce SiCl₄.

As was described above and will be described in more details below, BCl₃can be added as a gas (FIGS. 4 and 5) or can be generated in situ (FIG.3) through reaction

B₂O₃+1.5C+3Cl₂=2BCl₃(g)+1.5CO₂(g)   (7)

The gaseous product 30 is collected in a pipe system connecting thechlorination reactor 14 to a first condensing unit 32 (FIGS. 3 and 4) ora primary condenser 132 (FIG. 5). The pipe system is thermostated, i.e.the gas temperature inside the pipe does not allow the condensation ofthe gas before it reaches the condenser unit. Thus, the temperature canbe maintained over the boiling/condensing temperature of GeCl₄ (84° C.)if the system includes a first condensing unit 32 (FIGS. 3 and 4) andabove the boiling/condensing temperature of SiCl₄ (57.6° C.) if thesystem includes a primary condenser 132 (FIG. 5). For a glassy residuefeed material, the boiling points of the other gaseous productcomponents exiting the carbochlorination reactor 14 are lower than GeCl₄boiling point. Thus, all gaseous product components remain in gaseousphase in the pipe system extending between the chlorination reactor 14and the first condensing unit 32 or the primary condenser 132.

First Condensing Unit: GeCl₄ (FIGS. 3 and 4)

If the feed material 10 includes glassy residues and thus the gaseousproduct 30 includes gaseous GeCl₄, the first condensing unit 32condenses selectively GeCl₄(g) from the other gaseous product componentsand, more particularly, SiCl₄(g), BCl₃(g), Cl₂(g), CO₂(g) as shown inFIGS. 1 and 2.

To perform this selective condensation of GeCl₄, the temperature insidethe condenser 32 is set to a set-point slightly below GeCl₄ boilingpoint and slightly above SiCl₄ boiling point (57.6° C.). The gaseousproduct 30 is cooled and washed with liquid GeCl₄ 38.

The condenser 32 is filled with perforated spheres made of a resistantmaterial. A recycling loop of liquid GeCl₄ connected to a shower nozzle,placed at the top of the unit, assures adequate percolation and contactsbetween the liquid phase 38 and the gaseous product 30. The condensedliquid GeCl₄ 40 is collected in a reservoir placed at the base of thecondensing unit 32. The gaseous product 42 exiting the condenser 32 isessentially composed of SiCl₄(g), BCl₃(g), Cl₂(g), and CO₂(g). It isdirected via a second pipe system to a second condensing unit 34 wheregaseous SiCl₄ is condensed, as it will be described in more detailsbelow.

As for the first pipe system extending between the chlorination reactor14 to the first condensing unit 32, the second pipe system isthermostated. Thus, the temperature can be maintained over SiCl₄ boilingtemperature (57.6° C.) and below GeCl₄ boiling point (84° C.). Thus, allgaseous product components remain in gaseous phase in the second pipesystem extending between the first and the second condensing units 32,34.

Primary Condenser (FIG. 5)

If the feed material 110 includes a SiO₂-rich material which issubstantially free of GeO₂, the first condensing unit 32 can be replacedby a primary condenser 132 as shown in FIG. 5 since the gaseous product30 is also substantially free of gaseous GeCl₄. It is appreciated thatthe first condensing unit 32 can be either by-passed or removed.

This primary condensing step is carried out for SiO₂-rich feed materialcontaining a substantial amount of other oxides than GeO₂. These oxidesas well as SiO₂ are transformed in chlorides and are transported outsidethe chlorination reactor 14 as gases. These chlorides (MCl_(x)) have tobe condensed separately from SiCl₄ to avoid contamination in thesubsequent process steps. Thus, the primary condenser 132 condenseschloride impurities, as a mixture, from the other gaseous productcomponents and, more particularly, SiCl₄(g), BCl₃(g), Cl₂(g), andCO₂(g).

To perform this selective condensation, the primary condenser 132 is influid communication with the chlorination reactor 14 and contains largesurface deflectors to collect these chloride impurities.

The temperature inside the primary condenser 132 is adjusted to beslightly above the boiling/condensing temperature of SiCl₄ (57.6° C.),in order to assure maximal removal of unwanted chlorides and to allowSiCl₄ to exit the primary condenser 132 as a gas 42.

The condensed chlorides 140 are collected in a reservoir placed at thebase of the primary condenser 132. The gaseous product 42 exiting thecondenser 132 is essentially composed of SiCl₄(g), BCl₃(g), Cl₂(g), andCO₂(g). It is directed via a second pipe system to a second condensingunit 34 where gaseous SiCl₄ is condensed, as it will be described inmore details below.

As for the first pipe system extending between the chlorination reactor14 to the primary condenser, the second pipe system is thermostated.Thus, the temperature can be maintained above SiCl₄ boiling temperature(57.6° C.). Thus, all gaseous product components remain in gaseous phasein the second pipe system extending between the primary condenser 132and the second condensing unit 34.

Second Condensing Unit: SiCl₄

This second condensing unit 34 is similar to the first condensing unit32, except that the temperature inside the condenser 34 is set to apoint slightly below SiCl₄ condensation point and above BCl₃condensation point and that the gaseous product 42 entering thecondenser 34 is washed with SiCl₄ in liquid phase 44. In an embodiment,the temperature inside the condenser 34 ranges between 15 and 25° C.These operating conditions allow the selective condensation of SiCl₄ 46which is collected in a reservoir located at the base of the condensingequipment 34. Hence, the gaseous product 48 exiting the second condenser34 essentially includes BCl₃(g), Cl₂(g), CO₂(g). It is directed towardsa third condensing unit 36 where the condensation of BCl₃ is carried outthrough a third pipe system.

As for the previous pipe systems, the third pipe system is thermostatedand its temperature is maintained over BCl₃ boiling temperature (12.5°C.) and below SiCl₄ boiling point (57.6° C.). Thus, BCl₃(g), Cl₂(g),CO₂(g), the gaseous product components, remain in gaseous phase in thethird pipe system extending between the second and the third condensingunits 34, 36.

Third Condensing Unit: BCl₃

In the third condensing unit 36, gaseous BCl₃ is condensed. Thetemperature inside the condenser 36 is adjusted to a set-point slightlybelow the condensation point of BCl₃ and the gas entering the condenser36 is washed with liquid BCl₃ 50 allowing its selective condensation. Inan embodiment, the temperature inside the condenser 36 ranges between 0and 10° C. The gaseous product 52 exiting the condenser 36 includesCl₂(g) and CO₂(g) and it is directed towards a scrubbing and aneutralization systems.

Liquid BCl₃ 56 obtained at this condensation step can be recycled as areagent 223 to the chlorination reactor 14 after a gasification step 58.The quantity of recycled BCl₃ 223 used to chlorinate the optical fiberfeed 10 and SiO₂ rich feed 110 are balanced with additional input ofBCl₃ 29 or solid boron compound 16, if necessary.

Scrubbing and Neutralization

Chlorine (Cl₂) is removed from the gaseous product 52 in a scrubber 54.This scrubbing unit 54 includes a vertical cylinder containingperforated plastic spheres. The scrubber 54 is filled to a certainextend with a solution of NaOH 60. A system, including a pump linked toa recycling loop and a spray nozzle located at the top of the scrubber54, allows the gaseous product 52 to be washed and contacted with theNaOH solution 60. The following reaction occurs between chlorinecontained in the gaseous product 52 and the NaOH solution 60:

Cl₂(g)+2NaOH═NaOCl+NaCl+H₂O.   (8)

The pH of the solution is controlled by an exterior supply ofconcentrated NaOH. The NaOCl solution 62 resulting from the scrubbingprocedure is subsequently treated with H₂O₂ 64, in an agitated tank 66,in order to obtain a sodium chloride solution 68 by the reaction

NaOCl+H₂O₂═NaCl H₂O+O₂.   (9)

The gas exiting at the top of the scrubber contains essentially CO₂ 70.If necessary, the CO₂ 70 exiting the process can be trapped orneutralized by an existing complementary technology aiming at CO₂emanation recovery.

Cl₂ Compressor

In an alternate embodiment, the chlorine scrubber unit 54 can bereplaced by a chlorine compressor which allows compression of gaseouschlorine into a liquid chlorine and therefore its separation fromgaseous CO₂. The compressed chlorine can be stored in gas cylinders forfuture uses such as one of the chlorination process reactant.

Liquid GeCl₄ and Liquid SiCl₄

The process described above transforms optical fibers glassy residues orany materials rich in SiO₂ in chloride forms which can be directly orindirectly used as feed material for manufacturing optical fibers,various electronic components or solar panels. The liquid tetrachloridesselectively separated during the process and collected at the base ofthe GeCl₄ condenser and the SiCl₄ condenser are of relatively highpurity.

If necessary, additional purification steps can be performed on theseparated tetrachlorides obtained from the process. These additionalpurification steps can include one or several methods such asdistillation, fractional distillation, solvent extraction, resinpurification or by a common ion effect.

Alternative Embodiment (FIG. 6)

Alternatively, the gas leaving the reactor 14 and containing SiCl₄ andGeCl₄ is condensed in a single condenser unit 44. After thiscondensation step, the components of liquid mixture obtained areseparated by fractional distillation 76 providing a means to obtain pureSiCl₄ 72 and GeCl₄ 74.

Condensing the gaseous phase exiting the reactor into a suitablecondenser as a liquid is achieved at a temperature whereas the gas vaporpressure is sufficiently low for obtaining a liquid containing Cl₂,BCl₃, SiCl₄ and GeCl₄. The obtained liquid is then transferred to afractional distillation column.

If necessary, the gaseous phase exiting the condenser is neutralizedinto a scrubber 54 whereas Cl₂ is transformed to NaOCl 62, and residualBCl₃, SiCl₄ and GeCl₄ to their corresponding oxides and/or hydroxides.

The fractional distillation column is operated in such a way thatfirstly Cl₂ is condensed from the top of the column. When Cl₂ iscompletely removed from the mixture, the operational parameters aremodified to obtain BCl₃ 56 at the top of the column which is alsocondensed independently. After the complete removal of BCl₃ from themix, the parameters are adjusted to obtain pure SiCl₄ 72 at the top ofthe column which is collected separately. At the end of the distillationstep for SiCl₄, the bottom flask contains only GeCl₄ 74. Such adistillation procedure allows the recovery of four independent liquidcompounds Cl₂, BCl₃, SiCl₄ and GeCl₄.

Liquid Cl₂ can then be recycled as a reacting agent for the processafter a suitable gasification step. Liquid BCl₃ can also be recycled asa reacting agent for the process after a suitable gasification step.

Experimental Set Up (FIGS. 7 and 8)

Referring to FIGS. 7 and 8, there is shown an experimental set up forcarrying out the processes described above. The experiments wereperformed into a cylindrical horizontal reactor 310 including a quartztube having an inert lining and heated by an electrical furnace 312, asreaction tube. Cylinders of Cl₂, BCl₃ and N₂ gases 314 were connected tothe reaction tube 310. Pressure regulators and mass flow controllers 316were used to obtain a quantitative distribution of gases into thereaction tube 310 (FIG. 7). Gases leaving the reactor 310 were scrubbedin a scrubber 318 by a NaOH solution, which was periodically changed.CO_((g)) and CO_(2(g)), were not neutralized by the scrubber 318 andwere evacuated by the laboratory fume hood (not shown).

A small number of experiments were conducted using CO as a reducingagent. In these cases, a fourth gas bottle and a corresponding massflowcontroller were added to the experimental set-up.

In a typical experiment, the following steps were carried out. A giventype of an optical preform residue was grinded to minus 20 μm. Thisgrinded material was placed in a beaker 320 (FIG. 8), if necessary, asit will be described in more details below in reference to equations 10and 11, a solid reducer was added as well as H₃BO₃ (directly or adsorbedon the solid reducer). Alternatively, the grinded material was placed inbeaker 320, and if necessary, a solid reducer was added with or withoutKCl, as salt for the reagent mixture.

The beaker 320 was positioned in the center of the reaction tube 310(FIG. 8). N₂ flowed in the system and the solid was dried for a periodof one hour at a temperature of 500 C. At the end of the drying step,the furnace temperature was set between 450° C. and 1100° C. When thereaction temperature was reached, the flow of N₂ was stopped and Cl₂flowed into the system at a total flowrate varying from 0.1 to 0.4 literper minute with or without CO or BCl₃ as required. When CO was used theflowrate ratio Cl₂/CO was set to one for most experiments. When BCl₃ wasused the flowrate was set to 0.1 liter per minute. After a given periodof time, GeCl₄(g) and SiCl₄(g) were produced, exited the furnace 312 andwere scrubbed.

The conversion rates of GeO₂ and SiO₂ for a given experiment werecalculated from the mass variations in GeO₂ and SiO₂ between the massesinitially present and those observed at the end of the experiment in thesolid residue left in the beaker 320. The mass variations wereattributed to the transformations of GeO₂ and SiO₂ into their respectivetetrachlorides (GeCl₄ and SiCl₄). These tetrachlorides, being volatilein the temperature range investigated, were carried outside the beaker320 containing the preform sample and were scrubbed by the NaOHsolution. The mass variations were calculated from the weight of thesample and the solid residue combined to the respective concentrationsof GeO₂ and SiO₂. The analyses were realized by fusion with lithiummetaborate followed by dissolution in HNO₃ and HCl, the resultingliquids were analyzed by inductively coupled plasma atomic emissionspectroscopy (ICP-AES).

TABLE 1 Experimental parameters and results. Quantity Mass Boron # TimeTemperature preform Boron compound Experiment Beaker type (min) Stirring(° C.) (g) compound (g) Type solid Reducer 1 Fused Quartz 30 Ø 7000.2502 H₃BO₃ 0.2502 Ø 2 Fused Quartz 60 Ø 700 0.2502 No Ø MetallurgicalCoke 3 Fused Quartz 90 Ø 700 0.2645 H₃BO₃ 0.2645 Metallurgical Coke 4Fused Quartz 90 Ø 850 0.2536 Non Ø Ø 5 Fused Quartz 30 Ø 850 0.2576H₃BO₃ 0.2576 Metallurgical Coke 6 Fused Quartz 60 Ø 850 0.2657 H₃BO₃0.2657 Metallurgical Coke 7 Fused Quartz 60 Ø 1000 0.2542 H₃BO₃ 0.2542 Ø8 Fused Quartz 13 Ø 1000 0.2534 H₃BO₃ 0.2533 Metallurgical Coke 9 FusedQuartz 90 Ø 1000 0.2672 H₃BO₃ 0.2672 Metallurgical Coke 10  Fused Quartz30 Ø 1000 0.2603 No Ø Metallurgical Coke 11  Graphite 20 Ø 850 0.2514B₂O₃ 0.2664 Activated charcoal on activated charcoal 12  Ceramic 60 Ø850 0.2530 B₂O₃ 0.2665 Activated charcoal on activated charcoal 13 Graphite 20 + 2 850 0.2512 B₂O₃ 0.2664 Activated charcoal 20 + on 20activated charcoal Mass Flowrate Conversion Conversion solid gaseousFlowrate rate rate # reducer Gaseous Reducer Cl₂ SiO₂ GeO₂ Experiment(g) reducer (L/min) (L/min) (%) (%) 1 Ø CO 0.4 0.4 24 2 0.5004 Ø Ø 0.4 33 0.5290 CO 0.4 0.4 24 4 Ø CO 0.4 0.4 1 5 0.5152 Ø Ø 0.4 29 6 0.5314 CO0.4 0.4 25 7 Ø CO 0.4 0.4 7 8 0.5064 Ø Ø 0.4 30 9 0.5343 Ø Ø 0.4 30 10 0.5207 CO 0.4 0.4 6 11  1.7360 Ø Ø 0.4 67 79 12  1.7361 Ø Ø 0.4 65 7613  1.7355 Ø Ø 0.4 72 84

TABLE 2 Experimental parameters and results. Mass Type of Mass of BoronMass of Sample Time Partial Temperature Sample SiO₂ Boron addition (g)or Type of reducing Reducing number (min) mixing (° C.) type (g)addition L/min KCl %⁻¹ agent agent (g)  1 30 Ø 850 Preform 0.2503 BCl₃0.1 L/min 23 Darco 20X40 0.8642  2 30 Ø 850 Preform 0.5000 BCl₃ 0.1L/min 13 Darco 20X40 0.9000  3 30 Ø 850 Preform 0.2501 BCl₃ 0.1 L/min 23Darco 20X40 0.8643  4 30 Ø 850 Preform 0.9006 BCl₃ 0.1 L/min 13 Darco20X40 0.9002  5 30 Ø 850 Preform 0.2502 BCl₃ 0.1 L/min 14 Darco 20X401.7288  6 60 Ø 850 Preform 0.2502 BCl₃ 0.1 L/min 14 Darco 20X40 1.7285 7 30 Ø 850 Preform 0.9006 BCl₃ 0.1 L/min 13 Darco 20X40 0.4506  8 30 Ø850 Preform 0.2504 BCl₃ 0.1 L/min 12 Darco 20X40 1.7285  9 30 Ø 850Preform 0.2501 BCl₃ 0.1 L/min  7 Darco 20X40 1.7285 10 30 Ø 700 Preform0.2505 BCl₃ 0.1 L/min 14 Darco 20X40 1.7288 11 30 Ø 850 Preform 0.2505BCl₃ 0.1 L/min  4 Darco 20X40 1.7377 12 30 Ø 850 Preform 0.2501 BCl₃ 0.1L/min Ø Darco 20X40 1.7289 13 30 Ø 850 Preform 0.2501 BCl₃ 0.1 L/min Ø Ø0.0000 14 30 Ø 850 Preform 0.2500 B₂O₃ AC 0.5000 12 Darco 20X40 1.728515 30 Ø 850 Preform 0.2505 B₂O₃ AC 0.4998 Ø Darco 20X40 1.7281 16 30 Ø1000 Preform 0.2603 Ø Ø Ø Metallurgical Coke 0.5207 17 60 Ø 700 Preform0.2502 Ø Ø Ø Metallurgical Coke 0.5004 18 90 Ø 850 Preform 0.2536 Ø Ø ØØ Ø Addition CO Cl₂ Sample weight sample weight Weight ConversionConversion Sample of Flow Flow before after loss rate rate number CO(L/min) (L/min) reaction (g) reaction (g) (%) SiO₂ (%) GeO₂ (%)  1 Ø Ø0.4 1.4489 0.7637 47.29 98 96  2 Ø Ø 0.4 1.6105 0.5589 65.30 98 99  3 ØØ 0.4 1.4491 0.6818 52.95 98 97  4 Ø Ø 0.4 2.0711 0.4779 76.93 97 99  5Ø Ø 0.4 2.3135 1.5271 33.99 96 96  6 Ø Ø 0.4 2.3133 1.4153 38.82 95 97 7 Ø Ø 0.4 1.5537 0.1424 90.83 94 95  8 Ø Ø 0.4 2.2491 1.6148 28.20 8896  9 Ø Ø 0.4 2.1171 1.5011 29.10 85 95 10 Ø Ø 0.4 2.3138 1.9136 17.3072 72 11 Ø Ø 0.4 2.067 1.6094 22.14 71 78 12 Ø Ø 0.4 1.979 1.6235 17.9661 68 13 CO 0.4 0.4 0.2501 0.1370 45.22 51 49 14 Ø Ø 0.4 2.8128 1.427449.25 79 78 15 Ø Ø 0.4 2.4784 1.448 41.58 60 64 16 CO 0.4 0.4 0.7810.7107 9.00 6 NA 17 Ø Ø 0.4 0.7507 0.7143 4.85 3 NA 18 CO 0.4 0.4 0.25360.2487 1.93 1 NA ⁻¹(mass of KCl/total mass of the sample) × 100 NA: notanalyzed B₂O₃ AC: B₂O₃ adsorbed on activated charcoal

EXAMPLES

For all experiments, the experimental parameters used and the conversionrates obtained are reported in Tables 1 and 2. The experiments of Tables1 and 2 were conducted with an optical fiber preform containing 99 wt %SiO₂ and 1 wt % GeO₂. The specific examples described below containadditional experimental details.

To evaluate the effect of the reducer nature, another chlorinationprocess, referred here as the high temperature process, was carried out.This high temperature process uses chlorine gas or HCl gas incombination with a CO gas reducing agent to transform oxides phases inchlorides and, more particularly, to transform the components of opticalfibers in their chloride precursors, GeCl₄ and SiCl₄. The reactionsoccurring at the carbochlorination step being:

GeO₂+2Cl₂(g)+2CO(g)=GeCl₄(g)+2CO₂(g)   (10)

and

SiO₂+2Cl₂(g)+2CO(g)=SiCl₄(g)+2CO₂(g).   (11)

The experiments were conducted at 1200° C. showed that less than 5% ofSiO₂, one of the two main chemical targets, was converted to a chlorideform. Thus, this high temperature process was considered relatively nonefficient.

Example 1 Identification of the Main Parameters Influencing theSimultaneous Conversion of GeO₂ and SiO₂ into GeCl₄ and SiCl₄

In order to minimize the number of experiments to identify the mainparameters controlling the conversion of GeO₂ and SiO₂ into GeCl₄ andSiCl₄ an orthogonal matrix of the Taguchi type was constructed usingfour parameters: a) reaction time, b) reaction temperature, c) additionof boron, d) type of reducer. The reaction time was varied from 20 to 90minutes. The temperature was varied from 700° C. to 1200° C. The solidreducers tested were metallurgical coke and gaseous CO. Boron was addeddirectly as H₃BO₃. The parameters tested and the conversion ratesobtained, according to the pre-defined orthogonal matrix, are reportedat Table 1 under experiments No. 1-10. For these experiments only theconversion factor for SiO₂ was considered has being of significance forthe variance analysis since the analytical errors on GeO₂ conversionrates were superior to those for SiO₂ and were introducing additionalerrors for the determination of the influent parameters. High conversionrates for SiO₂ tend to favor higher conversion rates for GeO₂ because ofthe physical nature of GeO₂—SiO₂ glasses. More particularly, the maincomponent, SiO₂, is effectively removed as a gas and therefore itexposes GeO₂ to the chemical reactants present in the reactor. Theconversion rates for SiO₂ varied from 1 to 30% depending on theexperimental conditions. The variance analysis for the parameters testedwas calculated using the Optimum software distributed by TDC software.

Three important observations resulted from the analysis carried. First,the addition of boron as H₃BO₃ was always linked to the highest SiO₂conversion rates. This parameter alone accounted for 66% of the variancebetween all results. This observation is consistent with experimentaldata available from the scientific literature, as described above in thechlorination section. Second, metallurgical coke as a reducer was moreefficient than CO alone or combined with metallurgical coke. Third, thereaction time within the selected matrix range, i.e. from 30 to 90minutes, appeared to have little influence on the SiO₂ conversion rates.

The second and the third observations are related. Solid carbonaceousreducing agents, such as metallurgical coke, tend to acceleratechlorination reactions. This is attributed to the formation of atomicchlorine or activated chlorine species at their surfaces followed bydesorption. These species then react with the surface of the compoundtargeted for chlorination (Korshunov, 1992, Metallurgical Review ofMMIJ, 8, (2), pp. 1-33). The distance between a given carbonaceous solidreducer and an oxide surface is important. If this distance increases toa certain level, the atomic chlorine or activated chlorine liberated inthe gas phase can recombine, as the result of particle collisions, andbecome deactivated. During the chlorination reactions, the carbonaceousreducer surfaces in contact or near the oxides are consumed andtherefore the distances separating the solid reducers and the oxides areconstantly increasing and eventually reach a point where theconcentrations of atomic chlorine or activated chlorine species are lowdue to recombination reactions. The reaction speeds are then lowered andproceed via a mechanism involving molecular chlorine (Barin and Schuler,1980, Metallurgical Transactions B, 11B, pp. 199-207). For a givenchlorination reaction conducted in a static reactor involving carbon asa solid reducer, two kinetic zones are thus recognizable. An initiallyrapid one characterized by fast reaction kinetics driven by atomicchlorine or activated chlorine species. A later slow one characterizedby slow reaction kinetics conducted via molecular chlorine. It isprobable that the selected reaction times where such that thechlorination reactions had already reached the slow kinetic zone showingonly minor gains in the conversion rate of SiO₂ with time.

These observations were used to design experiments in order to increasethe conversion rates of GeO₂ and SiO₂. Equations 5 to 7 shows that onlyequation 7 requires the use of chlorine in the presence of acarbonaceous solid reducer. Once that BCl₃ is formed it is assumed thatthe reactions with GeO₂ and SiO₂ will occur rapidly and will not proceedthrough a diffusion mechanism implying atomic chlorine or activatedchlorine species. BCl₃ is a very strong Lewis acid (Alam et al., 2004)and should react very rapidly with the two free electron pairs on eachoxygen atom of GeO₂ and SiO₂. Kinetic optimization of reaction 9,assuming BCl₃ formation is the slow step, should increase the entirekinetic of the chemical system. The next example illustrates the effectsof the optimization of BCl₃ formation on the conversion rates of GeO₂and SiO₂.

Example 2 Optimization of BCl₃ Formation and its Effects on theConversion Rates of GeO₂ and SiO₂

In order to maximize contact between a given boron compound and thecarbonaceous solid reducer, a solution saturated with boric acid wasplaced in a beaker with activated charcoal. The pulp was then agitatedand filtered. The solid residue obtained was dried over night in an ovenat 150° C. The resulting activated charcoal doped with boron was usedfor the experiments.

It is known that BCl₃ react vigorously with water, in fact with anycompounds containing oxygen as explained above. To minimize sidereactions of BCl₃ with water an addition to the experimental procedurealready described was effected. The reagent, placed in the furnace, wasdried at 500° C. for 3 hours under a nitrogen atmosphere before beingexposed to the chlorine gas. The experimental parameters and the resultsfor these experiments are reported in Table 1 under experiments No. 11and 12. For these two experiments, the conversion rates for GeO₂ arehigh, 79% and 76% respectively for experiments 11 and 12. Similarly theconversion rates for SiO₂ are also high, 67% and 65% respectively forexperiments 11 and 12. As expected, there is a direct relationshipbetween GeO₂ and SiO₂ conversion rates. Comparatively to experiment 11,the reaction time was increased from 20 to 60 minutes in experiment 12.No important conversion rate improvement was observed; the conversionrates obtained for experiment 12 were within analytical errors of thoseof experiment 11.

Example 3 Effect of a <<Simulated Partial Mixing>> on the ConversionRates of GeO₂ and SiO₂

Experiments 1 to 12 were carried inside a static horizontal reactor. Itwas not possible to revise FIG. 7 experimental set up into a dynamicarrangement without introducing major modifications to the system.However, in experiment 13, the experimental procedure was adapted inorder to simulate one or several partial mixing episodes.

After a given reaction time, the chlorine flow was turned off and N₂ wasflowed into the quartz reaction tube. The furnace temperature waslowered from the predetermined experimental temperature to 350° C. Thebeaker containing the powder was withdrawn from the furnace still hotusing a glass rod. The powder was then mixed with a glass spoon for fewminutes under a fume hood. The beaker containing the powder was thenreplaced in the furnace, the temperature was adjusted to thepredetermined experimental temperature and a current of N₂ wasmaintained into the reaction tube. When the predetermined experimentaltemperature was reached, N₂ was turned off and Cl₂ flowed in the system.

Experiment 13 of Table 1 presents the experimental parameters and theconversion rates obtained. In this specific experiment, two partialmixing episodes were realized, each after a 20 minutes period ofreaction time. The total reaction time under chlorine atmosphere was 60minutes. The conversion rates obtained for GeO₂ and SiO₂ wererespectively 84% and 72%. Those results are directly comparable toexperiment 12 for which all experimental parameters are equivalent toexperiment 13 except that no partial mixing was involved. Thiscomparison indicates that the simulated partial mixing resulted into an8% increase in the conversion rate of GeO₂, from 76 to 84%, and into a7% increase in the conversion rate for SiO₂, from 65 to 72%. Clearlymixing has a positive impact on the conversion rates.

As previously discussed in Example 1, any chemical methods, such asadsorption, or physical methods, such as mixing, increasing contactsbetween oxides particles and carbonaceous solid reducer particles appearto enhance the global efficiency of the chlorination procedure.

The technology describes above allows the production of high puritychlorides from glassy residues originating from optical fibersmanufacturing or isolated from wasted optical cables.

It allows to produce directly GeCl₄ and SiCl₄ from the customarycomponents of optical fibers glassy residues, GeO₂ and SiO₂, without theformation of intermediate components such as silicon and elementalgermanium. Also, GeCl₄ and SiCl₄ obtained are isolated from one anotherand can be used as primary reactants in the dechlorination reactions forsuch processes as MCVD, ODS, AVD and other related methods.

GeO₂ and SiO₂, contained in glassy residues of optical fibers, areconcurrently extracted from glassy residues of optical fibers as GeCl₄and SiCl₄ respectively. Moreover, they are extracted as gaseous GeCl₄and SiCl₄ which leave the reaction reactor as gases.

The gaseous GeCl₄ and SiCl₄ leaving the reactor are condensedseparately, as liquids, in the appropriate condensers placed at the exitof the chlorination reactor. The first condenser extracts and condensesmainly GeCl₄ whereas the second condenser extracts and condenses mainlySiCl₄.

GeCl₄ and SiCl₄ obtained can be directly used as high purity chemicalsfor the production of optical fibers or others processes requiring highpurity chemicals. Alternatively, GeCl₄ and SiCl₄ obtained can besubmitted to an already existing purification procedure, such asfractional distillation, in order to reach the purity level needed.

Procedures are also available for the neutralization and/or therecycling of the chemicals needed in the process.

Example 4 BCl₄ ⁻ as Chlorination Agent

Although chlorination reactions can be conducted in numerous ways, it isrecognized that carbonaceous solid reducing agents such as metallurgicalcoke and activated charcoal tend to accelerate chlorination reactions.This is attributed to the formation of atomic chlorine, activatedchlorine species or ionic chlorine (Cl⁻ and/or Cl⁺) at their surfacesfollowed by desorption. These species, herein referred to as activechlorine, then react with the surface of the compound targeted forchlorination (Korshunov, 1992, Metallurgical Review of MMIJ, 8, (2), pp.1-33).

The distance between a given carbonaceous solid reducer and an oxidesurface is also relatively important. If this distance increases above acertain threshold, the active chlorine liberated in the gas phase canrecombine and deactivate. During chlorination reactions, thecarbonaceous reducer surfaces in contact or near the oxides are consumedand therefore the distance separating the solid reducer and the oxidesis constantly increasing during the chlorination reaction process andeventually reaches a point where the active chlorine concentrations arelow due to recombination reactions. The reaction speed thus slows downand the reaction proceeds via a mechanism involving molecular chlorine(Barin and Schuler, 1980, Metallurgical Transactions B, 11B, pp.199-207).

Thus for chlorination reactions, a rapid kinetic is first associated tothe formation of active chlorine and second to the stability over timeof active chlorine. The experiment designs were based on these twoobservations to obtain high conversion rates for SiO₂ and GeO₂.

The action of BCl₃ on SiO₂ to produce SiCl₄ and B₂O₃ was recognized at atemperature around 350° C. (See for instance Kroll, Metal Industry,1952, 81, (13), 243-6; Savel'ev et al., Neorganicheskie Materialy, 1973,9, (2), 325-6). B₂O₃ can be chlorinated (or regenerated) as BCl₃ by theaction of Cl₂ and a reducing agent such as coke or activated charcoal(Alam et al., 2004, Kirk-Othmer Encyclopedia of chemical technology,138-168). U.S. Pat. No. 4,490,344 discloses a combination of BCl₃, Cl₂and coke to produce SiCl₄ from SiO₂ in accordance with the followingreactions:

2BCl₃(g)+1.5 SiO₂=1.5 SiCl₄+B₂O₃   (6)

B₂O₃+1.5C+3Cl₂=2BCl₃(g)+1.5CO₂   (7)

These reactions are not carried out with active chlorine such as ionicchlorine (Cl⁻ and or Cl⁺). Moreover, the stability of active chlorine isnot considered in reactions 6, 7, 14 and 15.

In order to produce active chlorine and ion BCl₄ ⁻, BCl₃ was reactedwith KCl to produce the molten salt KBCl₄. The following chemical systemwas used to chlorinate SiO₂ and GeO₂:

KCl+BCl₃(g)=K⁺+BCl₄ ⁻(I)   (10)

4BCl₄ ⁻(I)+GeO₂+C═GeCl₄(g)+4BCl₃(g)+CO₂(g)   (11)

4BCl₄ ⁻(I)+SiO₂+C═SiCl₄(g)+4BCl₃(g)+CO₂(g)   (12)

BCl₃(g)+Cl₂(g)=BCl₄ ⁻+Cl⁺  (13)

K⁺+BCl₄ ⁻═KBCl₄   (14)

Cl⁺+C(negatively charged active sites)=C—Cl   (15)

To evaluate the chlorination reaction efficiency using BCl₄ ⁻, a seriesof experiments was carried out. The results are reported in Table 2 withsample numbers 1 to 11. The highest conversion rates were obtained forsamples 1 to 7. More particularly, the conversion rates for both SiO₂and GeO₂ in respectively SiCl₄ and GeCl₄ were equal to or higher than 94wt %. The reaction temperature was maintained at 850° C. and the KClcontent in the reagent mixture was varied from 13 to 23 wt %. Thereaction duration was varied between 30 to 60 minutes and the ratio(oxide mass)/(activated charcoal mass) was varied between 0.14 to 1. Forsample number 7, the ratio (oxide mass)/(activated charcoal mass) wasadjusted to 2. For this specific sample, the conversion rates for SiO₂and GeO₂ were respectively 94 wt % and 95 wt %.

Results from samples 8, 9, and 11 indicated that a decrease in the KCladdition resulted in lower conversion rates for SiO₂ and GeO₂. HigherSiO₂ and GeO₂ conversion rates were obtained for KCl addition rangingbetween 12 and 15 wt % and, in an embodiment, proximate to 13 wt %.

In sample 10, lowering the reaction temperature from 850° C. to 700° C.reduced the conversion rates to 72 wt % for both SiO₂ and GeO₂.

One experiment was stopped after 10 minutes and the SiO₂—GeO₂ glasseswere analyzed with a microprobe in order to search for the presence ofB₂O₃. B₂O₃ was not detected in the analyzed sample. This was interpretedhas an indication that the chlorination reactions were occurring inaccordance with reactions 10 to 15 without the intermediate formation ofB₂O₃.

These results show that the chlorination of SiO₂ and GeO₂ is efficientlyconducted with a reagent mixture including BCl₃, KCl, Cl₂ and activatedcharcoal, a chemical system promoting the formation of BCl₄ ⁻ aschlorination agent. Conversion rates equal to or higher than 94 wt % forboth SiO₂ and GeO₂ into their tetrachlorides SiCl₄ and GeCl₄ wereobtained at temperatures around 850° C. and for a reaction time ofapproximately 30 minutes.

Example 5 BCl₃ as Chlorination Agent

To demonstrate that the chemical system using BCl₄ ⁻ described in theprevious example is more efficient than one using BCl₃ as thechlorination agent (for example U.S. Pat. No. 4,490,344), experimentsusing a reagent mixture including BCl₃ but substantially free of KClwere conducted. Results are presented in Table 2 with sample numbers 12and 13.

Sample 12 was chlorinated under experimental conditions identical tosample 5 with exception that KCl was not added to the reagent mixture.For sample 12, the conversion rates for SiO₂ and GeO₂ were respectively61 wt % and 68 wt %. For sample 5 having a reagent mixture including 14wt % KCl, the conversion rates were 96 wt % for both SiO₂ and GeO₂.

These data clearly show the effect of the KCl addition in the reagentmixture. Addition of KCl in the reagent mixture leads to a 57% increasein the SiO₂ conversion rate and a 41% increase in the GeO₂ conversionrate. For sample number 13, the activated carbon in the reagent mixturewas replaced by CO. As for sample 12, the reagent mixture wassubstantially free of KCl. The conversion rates obtained were 51 wt %for SiO₂ and 49 wt % for GeO₂. Higher conversion rates for both SiO₂ andGeO₂ were obtained with activated carbon as solid reducer in the reagentmixture rather than CO.

Example 6 Chlorination with B₂O₃ as a Starting Chemical Component

BCl₃ can be produced by chlorination from B₂O₃ (Alam et al., 2004). Incertain circumstances, it could be advantageous to prepare BCl₃ fromB₂O₃ by chlorination, the produced BCl₃ being used as chlorinationagent. Experiments were conducted to investigate the effect of KCladdition in such cases.

As shown in FIG. 3 to prepare the solid reducer, a solution saturatedwith boric acid was placed in a beaker with activated charcoal. The pulpwas then agitated and filtered. The solid residue obtained was driedover night in an oven at 150° C. The resulting activated charcoal dopedwith boron was used for the chlorination experiments. It is known thatBCl₃ react vigorously with water. To minimize side reactions of BCl₃with water, an additional step was carried out in the experimentalprocedure. More particularly, the charge was dried in the furnace at500° C. for 3 hours under a nitrogen atmosphere before being exposed tothe reagent mixture including gaseous chlorine.

The experimental parameters and results for these experiments arereported in Table 2 with sample numbers 14 and 15. For sample 14 whereinthe reagent mixture includes 13 wt % KCl, the conversion rates obtainedfor SiO₂ and GeO₂ were respectively 79 wt % and 78 wt %. With a reagentmixture substantially free of KCl and for the same experimentalconditions, the conversion rates dropped to 60 wt % for SiO₂ and to 64wt % for GeO₂ in sample 15. Adding KCl in the reagent mixture lead to anincrease in the SiO₂ and GeO₂ conversion rates.

Example 7 Effect of Using Only Cl₂ and a Reducer

Experiments were also conducted using Cl₂ as the only chlorination agentin the presence of a reducer. Reducers tested were gaseous CO andmetallurgical coke. When CO is used, the reactions occurring in thecarbochlorination step are:

GeO₂+2Cl₂(g)+2CO=GeCl₄(g)+2CO₂(g)   (16)

SiO₂+2Cl₂(g)+2CO=SiCl₄(g)+2CO₂(g)   17)

When CO is replaced by metallurgical coke, the reactions are:

GeO₂+2Cl₂(g)+C═GeCl₄(g)+CO₂(g)   (18)

SiO₂+2Cl₂(g)+C═SiCl₄(g) CO₂(g)   (19)

Results reported in Table 2 under sample numbers 16 to 18 indicated thatthe conversion rates for SiO₂ are smaller than or equal to 6 wt %. It isprobable that the experimental conditions for samples 16 to 18 do notfacilitate the formation of a high active chlorine concentration.Therefore the efficiency of the chlorination is reduced when compare toexperimental conditions using a reagent mixture including KCl and BCl₃for similar reaction temperatures (850° C. and 1000° C.) and reactiontime.

The technology described above allows the production of high puritytetrachlorides from glassy residues originating from optical fibersmanufacturing or isolated from wasted optical cables. The technologyalso describes a method for the production of SiCl₄ from material richin SiO₂ and substantially free of GeO₂.

It allows to produce directly and concurrently GeCl₄ and SiCl₄ from thecustomary components of optical fibers glassy residues, GeO₂ and SiO₂,without the formation of intermediate components such as silicon andelemental germanium. Also, GeCl₄ and SiCl₄ obtained are isolated fromone another and can be used as primary reactants in the dechlorinationreactions for such processes as MCVD, ODS, AVD and other related methodssince they are identical to those commonly employed in the fabricationof optical fibers.

GeO₂ and SiO₂, contained in glassy residues of optical fibers, areconcurrently extracted from glassy residues of optical fibers as GeCl₄and SiCl₄ respectively. Moreover, they are extracted as gaseous GeCl₄and SiCl₄ which leave the reaction reactor as gases.

In an alternate embodiment, SiO₂ contained in a SiO₂-rich material richcan be transformed mainly in gaseous SiCl₄ which is subsequentlycondensed at the exit of the chlorination reactor.

The gaseous GeCl₄ and SiCl₄ leaving the reactor are condensedseparately, as liquids, in the appropriate condensers placed at the exitof the chlorination reactor. The first condenser extracts and condensesmainly GeCl₄ whereas the second condenser extracts and condenses mainlySiCl₄.

GeCl₄ and SiCl₄ obtained can be directly used as high purity chemicalsfor the production of optical fibers or others processes requiring highpurity chemicals. Alternatively, GeCl₄ and SiCl₄ obtained can besubmitted to an already existing purification procedure, such asfractional distillation, in order to reach the purity level needed.

Procedures are also available for the neutralization and/or therecycling of the chemicals needed in the process.

The embodiments of the invention described above are intended to beexemplary only. For example, it is appreciated that any means forrouting, transporting and transferring, solid, gas, liquid and pulpbetween the various process units can be used. The scope of theinvention is therefore intended to be limited solely by the scope of theappended claims.

1-5. (canceled)
 6. A method for producing GeCl₄ and SiCl₄ from opticalfibers, the method comprising the steps of: reacting comminuted opticalfibers including germanium and silicon oxides with a reagent including asolid carbonaceous reducing agent, chlorine and a boron compound toobtain a gaseous product including gaseous GeCl₄, gaseous SiCl₄, andgaseous BCl₃ in accordance with the reactions:2BCl₃(g)+1.5GeO₂=1.5GeCl₄(g)+B₂O₃2BCl₃(g)+1.5 SiO₂=1.5 SiCl₄(g)+B₂O₃B₂O₃+1.5C+3Cl₂=2BCl₃(g)1.5CO₂; by firstly condensing the gaseous GeO₄into liquid GeCl₄ by lowering gaseous product temperature below GeCl₄condensing temperature and above SiCl₄ condensing temperature; andsecondly condensing the gaseous SiCl₄ into liquid SiCl₄ by loweringgaseous product temperature below SiCl₄ condensing temperature and aboveBCl₃ condensing temperature.
 7. The method as claimed in claim 6,wherein the solid carbonaceous reducing agent is doped with the boroncompound.
 8. The method as claimed in claim 7, further comprisingadsorbing, in an agitated tank, the boron compound on the solidcarbonaceous reducing agent, from a solution including the boroncompound, to obtain the solid carbonaceous reducing agent doped with theboron compound; separating by filtration the solid carbonaceous reducingagent doped with the adsorbed boron compound from the solution; anddrying the solid carbonaceous reducing agent doped with the adsorbedboron compound before carrying the reacting step.
 9. The method asclaimed in claim 8, wherein the boron compound is H₃BO₃.
 10. The methodas claimed in claim 8, wherein the solution is saturated with the boroncompound.
 11. The method as claimed in claim 8, wherein the drying stepis carried out at a temperature ranging between 450 and 550° C.
 12. Themethod as claimed in claim 6, wherein the solid carbonaceous reducingagent is one of metallurgical coke and activated carbon.
 13. The methodas claimed in claim 6, wherein the boron compound comprises gaseousBCl₃. 14-32. (canceled)
 33. A method for producing SiCl₄ fromSiO₂-containing material, the method comprising the steps of: reactingcomminuted SiO₂-containing material with a reagent including a solidcarbonaceous reducing agent, a salt selected from the group consistingof: KCl, CsCl and RbCl, a boron compound, and chlorine (Cl₂) to obtain agaseous product including gaseous SiCl₄ in accordance with thereactions:4BCl₄ ⁻(I)+SiO₂+C═SiCl₄(g)+4BCl₃(g)+CO₂ condensing the gaseous SiCl₄into liquid SiCl₄ by lowering gaseous product temperature below SiCl₄condensing temperature.
 34. The method according to claim 33, whereinthe SiO₂-containing material is glassy residues.
 35. The methodaccording to claim 33, wherein the SiO₂-containing material furthercontain GeO₂ and the reaction also produces GeCl₄ according to thereaction:4BCl₄ ⁻(I)+GeO₂+C═GeCl₄(g)+4BCl₃(g)+CO₂ further comprising condensingthe gaseous SiCl₄ and GeCl₄ into liquid SiCl₄ and GeCl₄ by loweringgaseous product temperature below SiCl₄ and GeCl₄ condensingtemperatures.
 36. The method according to claim 33, wherein BCl₃ iscondensed along with condensing SiCl₄ by lowering gaseous producttemperature below SiCl₄ and BCl₃ condensing temperatures.
 37. The methodaccording to claim 33, wherein the produced GeCl₄ and SiCl₄ are used asstarting components for optical fiber manufacturing.
 38. The methodaccording to claim 33, wherein the chlorine (Cl₂) is absent.
 39. Amethod for producing SiCl₄ and GeCl₄ from optical fiber glassy residues,the method comprising the steps of: reacting comminuted optical fiberglassy residues with a reagent including a solid carbonaceous reducingagent, a salt selected from the group consisting of KCl, RbCl, and CsCl,chlorine and a boron compound to obtain a gaseous product includinggaseous GeCl₄ and gaseous SiCl₄ in accordance with the reactions:4BCl₄ ⁻(I)+GeO₂+C═GeCl₄(g)′4BCl₃(g)+CO₂4BCl₄ ⁻(I)+SiO₂+C═SiCl₄(g)+4BCl₃(g)+CO₂ firstly condensing the gaseousGeCl₄ into liquid GeCl₄ by lowering gaseous product temperature belowGeCl₄ condensing temperature and above SiCl₄ condensing temperature; andsecondly condensing the gaseous SiCl₄ into liquid SiCl₄ by loweringgaseous product temperature below SiCl₄ condensing temperature and aboveBCl₃ condensing temperature.
 40. The method as claimed in claim 33,wherein the ratio of solid carbonaceous reducing agent mass and glassyresidue mass ranges between 0.3 and
 1. 41. The method as claimed inclaim 33, wherein the ratio of salt mass and the sum of glassy residuemass, solid carbonaceous reducing agent mass, and salt mass rangesbetween 0.03 and 0.15.
 42. The method as claimed in claim 33, furthercomprising drying the comminuted glassy residues at a temperatureranging between 400 and 600° C. prior to carrying the reacting step. 43.The method as claimed in claim 33, wherein the solid carbonaceousreducing agent is one of metallurgical coke, graphite and activatedcarbon.
 44. The method as claimed in claim 33, wherein the boroncompound comprises gaseous BCl₃. 45-61. (canceled)
 62. A method forproducing SiCl₄ from glassy residues, the method comprising the stepsof: reacting glassy residues with a reagent including a solidcarbonaceous reducing agent, a salt selected from the group consistingof KCl, RbCl, and CsCl, chlorine and a boron compound to obtain agaseous product including gaseous SiCl₄; and condensing the gaseousSiCl₄ into liquid SiCl₄ by lowering the gaseous product temperaturebelow SiCl₄ condensing temperature.
 63. The method according to claim33, wherein the salt is KCl.